Conventionally, there is proposed a light emitting diode (LED) driving device for driving an LED unit where a plurality of LEDs are connected in series (for example, JP 2010-55824 A (hereinafter referred to as “Document 1”)).
The LED driving device of Document 1 includes a connecting means, a DC(direct-current)-to-DC converting means, a discharging means, and an ON-OFF switching means. The connecting means is detachably connected to the LED unit. The DC-to-DC converting means includes a smoothing capacitor, and is configured to convert the DC power supplied from a DC power supply. The discharging means includes a switching element, and is configured to form a discharge path for discharging the smoothing capacitor. The ON-OFF switching means is configured to switch between ON and OFF of the switching element of the discharging means.
In the LED driving device of Document 1, when the LED unit becomes detached from the connecting means, the ON-OFF switching means switches the switching element of the discharging means from an OFF state to an ON state. When the switching element of the discharging means is switched from the OFF state to the ON state, the smoothing capacitor of the DC-to-DC converting means is discharged. Thus, in the LED driving device, when the LED unit becomes detached from the connecting means, an output voltage of the DC-to-DC converting means can be decreased. This decrease can therefore prevent the phenomenon where an overcurrent flows through the LED unit when the LED unit is connected again.
In the LED driving device, however, when a second LED unit having a rated voltage relatively lower than that of a first LED unit is connected again, an overcurrent can flow through the second LED unit. In other words, the LED driving device further includes a controlling means. The controlling means is configured to stop the DC-to-DC converting means when the LED unit becomes detached from the connecting means and then the output voltage of the DC-to-DC converting means increases to a preset upper-limit threshold voltage. The upper-limit threshold voltage is set higher than a rated voltage of the LED unit in a steady state. Therefore, in the case where the second LED unit having a rated voltage relatively lower than that of the first LED unit is lit, when the second LED unit becomes detached from the connecting means, a long time is required until the switching element of the discharging means changes from an OFF state to an ON state. As a result, an overcurrent can flow through the second LED unit.